Protein synthesis is the step of gene expression that transfers genetic information from mRNA to protein. Accurate function of the protein synthesis apparatus is critical for this step. The elongation cycle performs the bulk of protein synthesis by adding all the subsequent amino acids after the initiator Met-tRNAiMet is placed in the ribosomal P-site during initiation. The translation elongation factor 2 (eEF2) is a member of the G-protein superfamily needed for the translocation of the peptide tRNA located in the ribosomal A-site to the P-site for continuation of the elongation of the peptide chain. Details of the molecular mechanism of the elongation cycle of protein synthesis have mostly come from studies in prokaryotic systems. But the greater complexity of eukaryotes is evident, and makes this an area of research where significant questions remain unanswered. The main difference between prokaryotic EF-G and eukaryotic eEF2 is the posttranslational modifications that happen to the latter, including phosphorylation of Thr57 and diphthamide modification of His699. The goal of this proposal is to utilize the yeast Saccharomyces cerevisiae for a coordinated genetic and biochemical analysis of the function and regulation of eEF2. A select group of eEF2 mutants designed for the analysis of the function of this protein will be analyzed in vivo and in vitro. This proposal focuses on increasing our understanding of the outcome of eEF2 regulation, the role of its translational modifications, and potential the effects of eEF2 in translation fidelity. [unreadable] [unreadable]